Color stabilization of vinyl halide copolymers



Patented Dec. 13, 1949 i E COLOR STABILIZATION OF VINYL IIALIDE coPoLYMERs Fred W. Cox, Birmingham, Ala., and .lames M.

Wallace, Jr., Akron, Ohio, assignors to Wingfoot Corporation, Akron, Ohio, a corporation of Delaware No Drawing. Application September 18, 1945, Serial No. 617,171

4 Claims.

This invention relates to the stabilization of copolymers of vinyl halide and particularly the vinyl halide resins which are copolymers of at least 70 percent of vinyl halide and at least 2 percent of another polymerizable mono-olefinic compound.

Vinyl halide copolymers generally will discolor when heated, for example at a temperature of 100 C. or higher. It has been discovered that the addition of a small proportion of a metallic nitrate or metallic nitrite will enable the resin to resist the discoloration efiect for substantial periods of time.

The vinyl halide copolymers which may be stabilized in accordance with this invention include copolymers of the vinyl halides of the group consisting of vinyl chloride, vinyl bromide, vinyl fluoride and vinyl iodide. The vinyl halide copolymers are copolymers of 70 to 98 percent of the vinyl halide and from 2 to 30 percent of another polymerizable mono-olefinic compound. Although any polymerizable mono-olefinic compound which is compatible with the vinyl halide in polymeric form, that is, which forms copolymers therewith, may be stabilized, the invention is particularly useful in the treatment of copolymers of monomeric mixtures of vinyl halide and from 2 to 30 percent of vinyl acetate, vinylidene chloride, styrene, the alkyl fumarates including the dialkyl maleates, the alkyl maleates, the alkyl chloro maleates including the dialkyl chloromaleates, the alkyl chloro fumarates including the dialkyl chlorofumarates, the alkyl acrylates, or the alpha substituted alkyl acrylates. The copolymers which are of particular importance are those of 80 to 95 percent of the vinyl halide and from 5 to 20 percent of the other monomer.

The stabilization against discoloration upon heating is effected by the addition of the metallic nitrate or nitrite. Although any member of these classes of compounds is useful, for reasons of economy the better known and less expensive salts are preferred, for example, sodium nitrate, sodium nitrite, potassium nitrate, potassium nitrite, ammonium nitrate, calcium nitrate, calcium nitrite, magnesium nitrate, zinc nitrate and lead nitrate. The quantity'of stabilizing agent used will depend upon the severity of the heating to which the vinyl copolymer will ultimately be subjected. Even traces of the agent will produce a beneficial effect where only mild heating is to be encountered. Although from 0.05 to 10 percent by weight, based on the copolymer content of the resin will produce useful compositions, generally 2 it is desirable to use from 0.5 to metallic nitrate or nitrite.

The stabilizing agent may be incorporated by any of several methods. It may be added to the solid copolymer and mixed therein by means of a roll mill or other mixing machine adapted to blend solid plastic materials. The mixing machine may be heated during the mixing operation to render the copolymers more plastic. Alternatively, the stabilizing agent may be dissolved in any suitable solvent and the solution then mixed with the copolymer. The vinyl halide copolymer may be dissolved in a solvent, such as ethylene dichloride, and the stabilizing agent added to the solution and dispersed therein by means of any stirring device. If the copolymers are prepared by polymerization in an aqueous emulsion, the stabilizing agent may be added and 5 percent of the distributed through the copolymer prior to coagulation. Any other method which permits a uniform distribution of the metallic nitrate or nitrite throughout the copolymer may be used.

The stabilizing copolymers may be used in the preparation ofcast films or in the fabrication of r molded or extruded shapes which uses are well known to the art. The vinyl halide copolymers stabilized with metallic nitrates or nitrites are particularly useful in the preparation of trans- Example Several 10 gram samples of a copolymer of 90 percent vinyl chloride and 10 percent diethyl fumarate were each milled with 2 ml. of dibutyl sebacate. Each of these samples was milled with 0.2 gram of one of the following materials: sodium nitrite, sodium nitrate, potassium nitrite,

potassium nitrate, calcium nitrate, magnesium nitrate, zinc nitrate, barium nitrate and bismuth nitrate.

trol for purposes of comparison and was not compounded with any metallic nitrite or nitrate. All of the copolymer samples were milled separately on a laboratory-size chromium-plated roll mill for 5 minutes at 140 F. and then for 5 minutes at 212 F. The copolymers were finally rolled into Test specimens were sheets 1 mm. in thickness. cut from each of the'copolymer sheets and were tested by heating at C. It wasfound that One of the samples was used as a con-' copolymer specimen which was not compounded with the metallic nitrates and nitrites was badly discolored.

This application is a continuation in part of' coloration upon heating which comprises a solid copolymer of 70 to 98 percent by weight of a vinyl halideand from 2 to 30 percent of an ester having the following structural formula.

wherein R is an alkyl radical, said copolymer con- 1 taining homogeneously dispersed therein from 0.05 to percent by weight, based on the copolymer content of the resin, of sodium nitrate.

2. A vinyl halide resin capable of resisting discoloration upon heating which comprises a copolymer of from 70 to 98 percent of a vinyl halide and from 2 to 30 percent of a dialkyl fumarate, said resin containing homogeneously dispersed therein from 0.05 to 5 percent by weight, based on the copolymer, of sodium nitrate.

3. A vinyl chloride resin capable of resisting discoloration upon heating which comprises a copolymer of to percent vinyl chloride and 5 to 20 percent of a dialkyl fumarate, said resin containing homogeneously dispersed therein from 0.5 to 5 percent by weight, based on the copolymer, of sodium nitrate.

4. A vinyl chloride resin capable of resisting discoloration upon heating which comprises a copolymer of 80 to 95 percent vinyl chloride and 5 to 20 percent of diethyl fumarate, said resin containing homogeneously dispersed therein from 0.5 to 5 percent by'weight, based on the copolymer, of sodium nitrate.

FRED W. COX. JAMES M. WALLACE, Jn.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,983,949 Semon Dec. 11, 1934 2,140,921 Rein Dec. 20, 1938 2,157,997 Brous May 9, 1939 2,222,928 Alexander Nov. 26, 1940 2,364,227 Lewis Dec. 5, 1944 2,377,752 Britten et a1 June 5, 1945 2,404,780 Arnold et a1 July 30, 1946 FOREIGN PATENTS Number Country Date 545,703 Great Britain June 5, 1945 

